The present invention relates to a refrigeration system, and more particularly to an apparatus and method for purging non-condensable gases from a refrigeration system.
In a conventional refrigeration system, particularly in low pressure centrifugal compressor systems, the leakage of air, water vapor, and other contaminating foreign gases into the system is a recognized problem. Such gases reduce the efficiency of the system since they tend to elevate the total pressure in the condenser, and thus more power is required from the compressor per unit of refrigeration. Also these foreign gases tend to cling to the condenser tubes thereby reducing the total condensing surface area.
To remove these foreign gases from the system, it is common practice to draw a mixture of the gaseous refrigerant and foreign gases from the high pressure region in the condenser or receiver where they normally accumulate, condense the refrigerant and any water vapor by cooling or by compression and cooling, vent off the non-condensables, separate and drain the water, and return the condensed refrigerant to the low pressure region of the system. The purge unit itself typically comprises a separation chamber wherein the non-condensables gather above the liquid refrigerant and water. A pressure actuated mechanical relief valve automatically opens to vent the non-condensables to the atmosphere through a gas discharge line, and a manual drain is provided to drain off the water which floats on top of the liquid refrigerant. A mechanical valve adjacent the bottom of the purge chamber is opened by a float when the refrigerant reaches a predetermined level to drain the refrigerant through a refrigerant line and return it to the low pressure region of the system.
U.S. Pat. No. 3,664,147 to Blackmon discloses a purge apparatus of the described type and which includes an electric float switch in the purge chamber and which is connected to a pair of solenoid actuated valves for (1) discharging a portion of the condensed refrigerant back through the refrigerant line to the low pressure region of the refrigeration system when the level of condensed refrigerant rises above a predetermined level, and (2) venting the non-condensable gases to the atmosphere through the gas discharge line when the level of the condensed refrigerant drops below a predetermined level. The apparatus described in the referenced patent has been commercialized in a configuration wherein a compressor is provided in the gas discharge line to facilitate withdrawal of the gas from the purge chamber, which is particularly useful when low operating pressures are utilized in the refrigeration system.
While the apparatus described in the above referenced patent is highly efficient, it is recognized that a small amount of non-condensed refrigerant may remain with the contaminating non-condensable gases in the purge chamber and be vented to the atmosphere through the gas discharge line during the purging operation.
It is accordingly an object of the present invention to further improve the efficiency of a purge apparatus of the described type by substantially eliminating the venting of any non-condensed refrigerant to the atmosphere during the purging operation.
It is a further object of the present invention to provide a purge apparatus of the described type which is economical to manufacture and which is effective and efficient in use.